Short-term impacts of Cu, CuO, ZnO and Ag nanoparticles (NPs) on anammox sludge: CuNPs make a difference

A review of microplastics on anammox: Influences and mechanisms

Microplastics (MPs) are prevalent in diverse environmental settings, posing a threat to plants and animals in the water and soil and even human health, and eventually converged in wastewater treatment plants (WWTPs), threatening the stable operation of anaerobic ammonium oxidation (anammox). Consequently, a comprehensive summary of their impacts on anammox and the underlying mechanisms must be provided. This article reviews the sources and removal efficiency of MPs in WWTPs, as well as the influencing factors and mechanisms on anammox systems. Numerous studies have demonstrated that MPs in the environment can enter WWTPs via domestic wastewater, rainwater, and industrial wastewater discharges. More than 90% of these MPs are found to accumulate in the sludge following their passage through the treatment units of the WWTPs, affecting the characteristics of the sludge and the efficiency of the microorganisms treating the wastewater. The key parameters of MPs, encompassing concentration, particle size, and type, exert a notable influence on the nitrogen removal efficiency, physicochemical characteristics of sludge, and microbial community structure in anammox systems. It is noteworthy that extracellular polymer secretion (EPS) and reactive oxygen stress (ROS) are important impact mechanisms by which MPs exposure affects anammox systems. In addition, the influence of MPs exposure on the microbial community structure of anammox cells represents a crucial mechanism that demands attention. Future research endeavors will delve into additional crucial parameters of MPs, such as shape and aging, to investigate their effects and mechanisms on anammox. Furthermore, the effective mitigation strategies will also be developed. The paper provides a fresh insight to reveal the influences of MPs exposure on the anammox process and its influence mechanisms, and lays the groundwork for further exploration into the influence of MPs on anammox and potential mitigation strategies.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f-=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

Strong suppression of silver nanoparticles on antibiotic resistome in anammox process

This study comprehensively deciphered the effect of silver nanoparticles (AgNPs) on anammox flocculent sludge, including nitrogen removal performance, microbial community structure, functional enzyme abundance, antibiotic resistance gene (ARGs) dissemination, and horizontal gene transfer (HGT) mechanisms. After long-term exposure to 0-2.5 mg/L AgNPs for 200 cycles, anammox performance significantly decreased (P < 0.05), while the relative abundances of dominant Ca. Kuenenia and anammox-related enzymes (hzsA, nirK) increased compared to the control (P < 0.05). For antibiotic resistome, ARG abundance hardly changed with 0-0.5 mg/L AgNPs but decreased by approximately 90% with 1.5-2.5 mg/L AgNPs. More importantly, AgNPs effectively inhibited MGE-mediated HGT of ARGs. Additionally, structural equation model (SEM) disclosed the underlying relationship between AgNPs, the antibiotic resistome, and the microbial community. Overall, AgNPs suppressed the anammox-driven nitrogen cycle, regulated the microbial community, and prevented the spread of ARGs in anammox flocs. This study provides a theoretical baseline for an advanced understanding of the ecological roles of nanoparticles and resistance elements in engineered ecosystems.

Soluble carbon source recovery using preconditioning coagulants for applicable short-term fermentation of waste activated sludge in WWTPs

A huge production of waste activated sludge (WAS) has been a burden for wastewater treatment plants (WWTPs) with high disposal cost and little benefit back to wastewater purification. The short-chain fatty acids (SCFAs) produced by a short-term acidogenic fermentation of WAS before methane production have been proven to be a high-quality carbon source available for microbial denitrification process. The dual purpose of full recovery of fermentation liquid products and facilitating disposal of residual solid waste necessitate an efficient solid-liquid separation process of short-term fermentation liquid. The transformation and loss of various soluble carbon sources between solid and liquid are very important issues for carbon recovery efficiency when combining short-term fermentation and sludge dewatering in WWTPs. Here we testified the three conventional preconditioning coagulants, Polyferric Sulfate (PFS), Poly Aluminum Chloride (PAC) and Polyacrylamide (PAM), to improve the efficiency of subsequent solid-liquid separation. The results show that conversion yield of SCFAs in the liquid phase of sludge after short-term fermentation was 195 mg COD/g VSS, when using the coagulants PFS, PAC, and PAM for recovery, the recovery ratio was 79.5%, 82.0%, and 85.9%, respectively, while the dewaterability could be improved after preconditioning short-term fermentation sludge. The complexation of Al3+/Fe3+ in metal coagulants with carboxyl groups of SCFA demonstrated by Density Functional Theory calculation led to small part of soluble carbons co-migration to the solid phase, mainly a loss of high molecular weight organic compounds (carbohydrate, proteins, humic acids), while the application of PAM had little impact on carbon recovery. Economic calculations further showed PAM preconditioning short-term fermentation liquid of WAS could achieve higher recovery benefits.

Synergistic antibacterial mechanism of silver-copper bimetallic nanoparticles

The excessive use of antibiotics in clinical settings has resulted in the rapid expansion, evolution, and development of bacterial and microorganism resistance. It causes a significant challenge to the medical community. Therefore, it is important to develop new antibacterial materials that could replace traditional antibiotics. With the advancements in nanotechnology, it has become evident that metallic and metal oxide nanoparticles (MeO NPs) exhibit stronger antibacterial properties than their bulk and micron-sized counterparts. The antibacterial properties of silver nanoparticles (Ag NPs) and copper nanoparticles (Cu NPs) have been extensively studied, including the release of metal ions, oxidative stress responses, damages to cell integrity, and immunostimulatory effects. However, it is crucial to consider the potential cytotoxicity and genotoxicity of Ag NPs and Cu NPs. Numerous experimental studies have demonstrated that bimetallic nanoparticles (BNPs) composed of Ag NPs and Cu NPs exhibit strong antibacterial effects while maintaining low cytotoxicity. Bimetallic nanoparticles offer an effective means to mitigate the genotoxicity associated with individual nanoparticles while considerably enhancing their antibacterial efficacy. In this paper, we presented on various synthesis methods for Ag-Cu NPs, emphasizing their synergistic effects, processes of reactive oxygen species (ROS) generation, photocatalytic properties, antibacterial mechanisms, and the factors influencing their performance. These materials have the potential to enhance efficacy, reduce toxicity, and find broader applications in combating antibiotic resistance while promoting public health.

Insights into heavy metals shock on anammox systems: Cell structure-based mechanisms and new challenges

Anaerobic ammonium oxidation (anammox) as a low-carbon and energy-saving technology, has shown unique advantages in the treatment of high ammonia wastewater. However, wastewater usually contains complex heavy metals (HMs), which pose a potential risk to the stable operation of the anammox system. This review systematically re-evaluates the HMs toxicity level from the inhibition effects and the inhibition recovery process, which can provide a new reference for engineering. From the perspective of anammox cell structure (extracellular, anammoxosome membrane, anammoxosome), the mechanism of HMs effects on cellular substances and metabolism is expounded. Furthermore, the challenges and research gaps for HMs inhibition in anammox research are also discussed. The clarification of material flow, energy flow and community succession under HMs shock will help further reveal the inhibition mechanism. The development of new recovery strategies such as bio-accelerators and bio-augmentation is conductive to breaking through the engineered limitations of HMs on anammox. This review provides a new perspective on the recognition of toxicity and mechanism of HMs in the anammox process, as well as the promotion of engineering applicability.

Accelerating the granulation of anammox sludge in wastewater treatment with the drive of "micro-nuclei": A review

Anammox granule sludge (AnGS) has great potential in the field of wastewater nitrogen removal, but its development and promotion have been limited by the slow granulation speed and fragile operating stability. Based on the reviews about the AnGS formation mechanism in this paper, "micro-nuclei" was found to play an important role in the granulation of AnGS, and adding "micro-nuclei" directly into the reactor may be an efficient way to accelerate the formation of AnGS. Then, accelerating AnGS granulation with inert particles, multivalent positive ions, and broken granule sludge as "micro-nuclei" was summarized and discussed. Among inert particles, iron-based particles may be a more advantageous candidate for "micro-nuclei" due to their ability to provide attachment sites and release ferric/ferrous ions. The precipitations of multivalent positive ions are also a potential option for "micro-nuclei" that can be generated in-situ, but a suitable dosing strategy is necessary. About broken granular sludge, the broken active AnGS may have advantages in terms of anaerobic ammonium oxidation bacteria-affinity and granulation speed, while using inactive granular sludge as "micro-nuclei" can avoid interfering bacterial invasion and has a higher cost performance than broken active AnGS. In addition, possible research directions for accelerating the formation of AnGS by dosing "micro-nuclei" were highlighted. This paper is intended to provide a possible pathway for the rapid start-up of AnGS systems, and references for the optimization and promotion of the AnGS process.

Use of nanoparticle-coated bacteria for the bioremediation of organic pollution: A mini review

Nanoparticle (NP)-coated (immobilized) bacteria are an effective method for treating environmental pollution due to their multifarious benefits. This review collates a vast amount of existing literature on organic pollution treatment using NP-coated bacteria. We discuss the features of bacteria, NPs, and decoration techniques of NP-bacteria assemblies, with special attention given to the surface modification of NPs and connection mechanisms between NPs and cells. Furthermore, the performance of NP-coated bacteria was examined. We summarize the factors that affect bioremediation efficiency using coated bacteria, including pH, temperature, and agitation, and the possible mechanisms involving them are proposed. From future perspectives, suitable surface modification of NPs and wide application in real practice will make the NP-coated bacterial technology a viable treatment strategy.

The roads taken and not taken: Trends of anammox-based wastewater treatment in China

•Grants supporting anammox for wastewater treatment in China was analyzed.•The next frontiers of anammox research are prospected.•Anammox-based biotechnologies potentially drives innovation in water sector.

Toxicity of synthesized silver nanoparticles in a widespread fish: A comparison between green and chemical

Metallic nanoparticles are gaining importance in various fields of life due to their large surface area to volume ratio. However, metallic nanoparticles pose different toxic effects on fish when they appear with different shapes and compositions in water. Herein the present study was designed to evaluate the median (LC₅₀) and sub-lethal (1/10th of LC₅₀) concentrations of Ag-Green NPs, 700 μg/L for Ag-Chem NPs, and 50 μg/L for Ag₂O-Chem NPs were confirmed in Hypophthalmichthys molitrix. Furthermore, exposure of H. molitrix fingerlings to 10 % of LC₅₀ concentration of these particles induced significantly higher (p < 0.05) activities of serum alanine transaminase, aspartate aminotransferase, lactate dehydrogenase, white blood cells, acetylcholinesterase and catalase, superoxide dismutase, peroxidase, relative gene expressions of antioxidant enzymes, heat shock protein (Hsp70), hypoxia- inducible factor 1-alpha (HIF-1α) and lipid peroxidase level than the control, but decreased hematological parameters with less effects of Ag-Green NPs than chemically synthesized AgNPs. Moreover, the histopathological study also indicated morphological changes in the liver and gills of treated fish groups. The comparative toxicity evaluation revealed the maximum negative effect of Ag₂O-Chem NPs followed by Ag-Chem NPs while Ag-Green NPs showed the least toxic effects. Based on our results, replacement of chemically synthesized NPs to green synthesized AgNPs can be recommended in large scale application to reduce the noxious effects to aquatic environment.

Removal of extracellular deoxyribonucleic acid increases the permeability and mass transfer of anammox granular sludge with different sizes

As a key component of extracellular polymeric substances (EPS), extracellular deoxyribonucleic acid (eDNA) acts as a bridge in maintaining the structural stability of granular sludge. However, its ability of carrying antibiotic resistance genes (ARGs) promotes the gene horizontal transfer, raising a high risk for human health. In this study, a series of batch tests were performed to elucidate the response of anammox granular sludge (AnGS) with different sizes (S-AnGS with diameters lower than 0.9 mm and L-AnGS with diameters of 0.9-2 mm) to the removal of eDNA and corresponding mechanism. The results showed that the highest bioactivity of S-AnGS and L-AnGS was achieved by adding DNase I, and the absolute abundance of hzsA in the systems also increased. The dominant microorganism in each sludge was Candidatus Kuenenia, which maintained a higher relative abundance of 24% in S-AnGS. Settling experiments demonstrated that the permeability of AnGS was positively correlated with the addition of DNase I. The permeability index of granular sludge, Г, rose by 58.54% in S-AnGS and 11.79% in L-AnGS. The absence of eDNA is conducive to the increase in the permeability and porosity of AnGS. Similarity in the functional genes and microbial communities of intracellular and extracellular DNA implied the occurrence of gene transmembrane transfer. The findings enrich our knowledge of eDNA in anammox granules and provide a guidance for the specific control of gene transfer through reducing eDNA.

The Aggregation and Dissolution of Citrate-Coated AgNPs in High Ammonia Nitrogen Wastewater and Sludge from UASB-Anammox Reactor

Silver nanoparticles (AgNPs) are released into the sewage pipes and ultimately wastewater treatment plants during manufacturing, use, and end-life disposal. AgNPs in wastewater treatment plants aggregate or dissolve, and may affect the microbial community and subsequent pollutant removal efficiency. This study aims to quantitatively investigate the fate of AgNPs in synthetic high ammonia nitrogen wastewater (SW) and sludge from an up-flow anaerobic sludge blanket (UASB) anammox reactor using a nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic absorption spectroscopy (AAS). Results showed that 18.1 mM NH4+, 2.11 mM Mg2+ in SW caused less negative zeta potential (ζ-potential, -18.4 vs. -37.4 mV), aggregation (388.8 vs. 21.5 nm), and settlement (80%) of citrate-coated AgNPs (cit-AgNPs) in 220 min. The presence of 18.5 mM Cl- in SW formed AgCl2-, AgCl(aq) and eventually promoted the dissolution (9.3%) of cit-AgNPs. Further exposure of SW-diluted AgNPs to sludge (42 mg L-1 humic acid) and induced a more negative ζ-potential (-22.2 vs. -18.4 mV) and smaller aggregates (313.4 vs. 388.8 nm) due to the steric and hindrance effect. The promoted Ag dissolution (34.4% vs. 9.3%) was also observed after the addition of sludge and the possible reason may be the production of Ag(NH3)2+ by the coexistence of HA from sludge and NH4+ from SW. These findings on the fate of AgNPs can be used to explain why AgNPs had limited effects on the sludge-retained bacteria which are responsible for the anammox process.

Flocculation with heterogeneous composition in water environments: A review

Flocculation is a key process for controlling the fate and transport of suspended particulate matter (SPM) in water environments and has received considerable attention in the field of water science (e.g., oceanography, limnology, and hydrology), remaining an active area of research. The research on flocculation has been conducted to elucidate the SPM dynamics and to diagnose various environmental issues. The flocculation, sedimentation, and transportation of SPM are closely linked to the compositional and structural properties of flocs. In fact, flocs are highly heterogeneous in terms of composition. However, the lack of comprehensive research on floc composition and structure has led to misconceptions regarding the temporal and spatial dynamics of SPM. This review summarizes the current understanding of the heterogeneous composition of flocs (e.g., minerals, organic matter, metals, microplastic, engineered nanoparticles) and its effect on their structure and on their fate and transport within aquatic environments. Furthermore, the effects of human activities (e.g., pollutant discharge, construction) on floc composition are discussed.

Performance and mechanism analysis of gel immobilized anammox bacteria in treating different proportions of domestic wastewater: a valid alternative to granular sludge

The treatment performance of anaerobic ammonia oxidation (anammox) immobilized filler on different proportions of domestic wastewater was evaluated. The results showed that, in comparison to synthetic wastewater, 50% domestic wastewater promoted the anammox reaction of immobilized filler, while 100% domestic wastewater had no significant effect on the anammox activity of immobilized filler but the total nitrogen removal efficiency (TNRE) was improved through enhanced denitrification. The TNRE of the immobilized filler was 82.5%, which was significantly higher than that of AnGS (69.7%), and its average anammox contribution rate was more than 90%. This was because the encapsulated anammox biomass could better maintain competitive advantages and coordinate the symbiotic relationship with denitrifying bacteria. Moreover, lower NH₄⁺-N concentration resulted in greater influence of C/N ratio on anammox performance than COD concentration, while the opposite was true at high NH₄⁺-N concentration. This study verified that anammox immobilized filler is effective for mainstream applications.

Comprehensive evaluation of the long-term effect of Cu2+ on denitrifying granular sludge and feasibility of in situ recovery by phosphate

With increased industrial development, vast heavy metals are inevitably discharged into wastewater. Cu²⁺ is one of the most hazardous heavy metals in biotreatment. However, the potential effect of Cu²⁺ on denitrifying granular sludge is still unknown. This work assesses the response of denitrifying granular sludge to Cu²⁺ stress from multiple aspects. The denitrifying granular sludge could tolerate 5 mg L^-1 Cu²⁺, while the nitrogen removal efficiency decreased to 48.5% under 10 mg L^-1 Cu²⁺. Enzyme activity and carbohydrate metabolism were inhibited, and the denitrifying bacteria were washed out under Cu²⁺ stress. The resulting deteriorated state was reversed by phosphate. The nitrogen removal efficiency recovered to 99% after 10 days, and the enzyme activity also recovered to the original level. Membrane transport, transcription and cellular processes were promoted. Overall, the results of this work provide a feasible strategy to rapidly restore the metabolic activity of denitrifying granular sludge under Cu²⁺ stress.

Inhibition of wastewater pollutants on the anammox process: A review

The anaerobic ammonium oxidation (anammox) process has been recognized as an efficient nitrogen removal technology. However, anammox bacteria are susceptible to surrounding environments and different pollutants, which limits the extensive application of the anammox process worldwide. Numerous researchers investigate the effects of various pollutants on the anammox process or bacteria, and related findings have also been reviewed with the focused on their inhibitory effects on process performance and microbial community. This review systemically summarized the recent advances in the inhibition, mechanism and recovery process of traditional and emerging pollutants on the anammox process over a decade, such as organics, metals, antibiotics, nanoparticles, etc. Generally, low-concentration pollutants exhibited a promotion on the anammox activity, while high-concentration pollutants showed inhibitory effects. The inhibitory threshold concentration of different pollutants varied. The combined effects of multipollutant also attracts more attentions, including synergistic, antagonistic and independent effects. Additionally, remaining problems and research needs are further proposed. This review provides a foundation for future research on the inhibition in anammox process, and promotes the proper operation of anammox processes treating different types of wastewaters.

Effect of metal and metal oxide engineered nano particles on nitrogen bio-conversion and its mechanism: A review

Metal and metal oxide engineered nano particles (MMO-ENPs) are widely applied in various industries due to their unique properties. Thus, many researches focused on the influence on nitrogen transformation processes by MMO-ENPs. This review focuses on the effect of MMO-ENPs on nitrogen fixation, nitrification, denitrification and Anammox. Firstly, based on most of the researches, it can be concluded MMO-ENPs have negative effect on nitrogen fixation, nitrification and denitrification while the MMO-ENPs have no promotion effect on Anammox. Then, the influence factors are discussed in detail, including MMO-ENPs dosage, MMO-ENPs kind and exposure time. Both the microbial morphology and population structure were altered by MMO-ENPs. Also, the mechanisms of MMO-ENPs affecting the nitrogen transformation are reviewed. The inhibition of key enzymes and functional genes, the promotion of reactive oxygen species (ROS) production, MMO-ENPs themselves and the suppression of electron transfer all contribute to the negative effect. Finally, the key points for future investigation are proposed that more attention should be attached to the effect on Anammox and the further mechanism in the future studies.

Recovery profile of anaerobic ammonium oxidation (anammox) bacteria inhibited by ZnO nanoparticles

The potential effects of nanoparticles (NPs) on biological treatment processes have become significant due to their increasing industrial applications. The purpose of this research was to investigate the self-recovery ability of anammox bacteria following acute ZnO NPs toxicity. In this context, a 2-liter lab-scale anammox reactor was operated for 550 days to enrich the biomass required to the batch exposure tests. Anammox culture was firstly exposed to four different doses of ZnO NPs (50, 75, 100 and 200 mg/L) for 24 h. Then, the ZnO NPs were removed and self-recovery performance of the anammox bacteria was assessed by evaluating the nitrogen removal capacities for 72 h. Besides the nitrogen removal performance, extracellular polymeric substances (EPS) production was also detected to deeply understand the response of the enriched anammox culture against ZnO NPs exposure. The results revealed that sudden and high load of ZnO NPs (100 and 200 mg/L) resulted in persistent impairment to the nitrogen removal performance of the enriched anammox culture. However, relatively lower doses (50 and 75 mg/L) caused deceleration of the nitrogen removal performance during the recovery period. In addition, EPS content in the reactor decreased along with escalating load of ZnO NPs.

Inhibition of anammox activity by municipal and industrial wastewater pollutants: A review

The use of the anammox process for nitrogen removal has gained popularity across the world due to its low energy consumption and waste generation. Anammox reactors have been used to treat ammonium-rich effluents such as chemical, pharmaceutical, semiconductor, livestock, and coke oven wastewater. Recently, full-scale installations have been implemented for municipal wastewater treatment. The efficiency of biological processes is susceptible to inhibitory effects of pollutants present in wastewater. Considering the increasing number of emerging contaminants detected in wastewater, the impacts of the different types of pollutants on anammox bacteria must be understood. This review presents a compilation of the studies assessing the inhibitory effects of different wastewater pollutants towards anammox activity. The pollutants were classified as antibiotics, aromatics, azoles, surfactants, microplastics, organic solvents, humic substances, biodegradable organic matter, or metals and metallic nanoparticles. The interactions between the pollutants and anammox bacteria have been described, as well as the interactions between different pollutants leading to synergistic effects. We also reviewed the effects of pollutants on distinct species of anammox bacteria, and the main toxicity mechanisms leading to irreversible loss of anammox activity have been identified. Finally, we provided an analysis of strategies to overcome the inhibitory effects of wastewater pollutants on the nitrogen removal performance. We believe this review will contribute with essential information to assist the operation and design of anammox reactors treating different types of wastewaters.

Impact of electro-conductive nanoparticles additives on anaerobic digestion performance - A review

Anaerobic digestion (AD) is a biochemical process that converts waste organic matter into energy-rich biogas with methane as the main component. Addition of electric electro-conductive, such as that nanoparticles (NP), has been shown to improve biogas generation. Interspecies electron transfer and direct interspecies electron transfer (DIET) using conductive materials is one of the mechanisms responsible for observed increases in CH₄. This article discusses the effect of the type and size of electro-conductive NPs on improving microbial degradation within AD systems, as well as the effect of electro-conductive NPs on microbial community shifts and syntrophic metabolism. Limitations and future perspectives of using NPs in an AD system is also discussed.

Effects of nano metal oxide particles on activated sludge system: Stress and performance recovery mechanism

Nano metal oxide particles (NMOPs) are widely used in daily life because of their superior performance, and inevitably enter the sewage treatment system. Pollutants in sewage are adsorbed and degraded in wastewater treatment plants (WWTPs) depending on the microbial aggregates of activated sludge system to achieve sewage purification. NMOPs may cause ecotoxicity to the microbial community and metabolism due to their complex chemical behavior, resulting in a potential threat to the safe and steady operation of activated sludge system. It is of great significance to clarify the influencing mechanism of NMOPs on activated sludge system and reduce the risk of WWTPs. Herein, we first introduce the physicochemical behavior of six typical engineering NMOPs including ZnO, TiO₂, CuO, CeO₂, MgO, and MnO₂ in water environment, then highlight the principal mechanisms of NMOPs for activated sludge system. In particular, the performance recovery mechanisms of activated sludge systems in the presence of NMOPs and their future development trends are well documented and discussed extensively. This review can provide a theoretical guidance and technical support for predicting and evaluating the potential threat of NMOPs on activated sludge systems, and promoting the establishment of effective control strategies and performance recovery measures of biological wastewater treatment process under the stress of NMOPs.

How anammox responds to the emerging contaminants: Status and mechanisms

Numerous researches have been carried out to study the effects of emerging contaminants in wastewater, such as antibiotics, nanomaterials, heavy metals, and microplastics, on the anammox process. However, they are fragmented and difficult to provide a comprehensive understanding of their effects on reactor performance and the metabolic mechanisms in anammox bacteria. Therefore, this paper overviews the effects on anammox processes by the introduced emerging contaminants in the past years to fulfill such knowledge gaps that affect our perception of the inhibitory mechanisms and limit the optimization of the anammox process. In detail, their effects on anammox processes from the aspects of reactor performance, microbial community, antibiotic resistance genes (ARGs), and functional genes related to anammox and nitrogen transformation in anammox consortia are summarized. Furthermore, the metabolic mechanisms causing the cell death of anammox bacteria, such as induction of reactive oxygen species, limitation of substrates diffusion, and membrane binding are proposed. By offering this review, the remaining research gaps are identified, and the potential metabolic mechanisms in anammox consortia are highlighted.

Effects of an organic carbon source on the coupling of sulfur(thiosulfate)-driven denitration with Anammox process

The sulfur(thiosulfate)-driven autotrophic denitrification coupled with Anammox (SDDA) process is proposed as an emerging technology for wastewater containing NH₄⁺-N and NO₃^--N. However, the influence of organic matter on the SDDA process is not fully understood. A long-term experiment has shown that a moderate organic (acetate) (＜140 mg/L COD) can accelerate the heterotrophic/autotrophic denitrification and Anammox activity, to reach as high as 92.8% ± 0.3% total nitrogen at a loading rate of 1.34 kg-N/(m³·d). Batch test results showed that Anammox made the largest contribution to the removal of nitrogen, even in an SDDA system with COD addition. Additionally, organics can promote the bioavailability of solid sulfur through reaction with sulfide to form polysulfides, which increased nitrite accumulation to forward Anammox process. Sulfur-oxidizing bacteria (e.g., Thiobacillus and Denitratisoma) coexisted with Anammox bacteria (e.g., Ca. Brocadia and Ca. Kuenenia) in the SDDA system despite the addition of exogenous COD.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

Anaerobic fermentation metabolism of Moorella thermoacetica inhibited by copper nanoparticles: Comprehensive analyses of transcriptional response and enzyme activity

Engineered nanoparticles are observed to be released into the environment and ended up in wastewater treatment plants. It has been reported that these nanoparticles in sewage might have a toxic effect on microorganisms, and thus affect anaerobic microbial fermentation. However, the mechanisms involved in nanoparticles-induced effects on the anaerobic acidification process and its related bacterial metabolism are still unclear. This work indicated that copper nanoparticles (Cu NPs) were able to cause cell membrane oxidative damage and inhibit the growth and metabolism of Moorella thermoacetica (a model acetogen). The OD₆₀₀ and acetic acid production of M. thermoacetica in the presence of 1 mg/L of Cu NPs were decreased to 29.2% and 40.7% of the control, respectively. The key mechanism of the inhibitory effect was governed by the fact that Cu NPs significantly reduced the glucose consumption, and led to the decreased pyruvate metabolism levels. Additionally, Cu NPs inhibited the gene expressions and catalytic activities of the key enzymes related to acetic acid production. It was identified that the relative activities of phosphofructokinase, pyruvate kinase, phosphotransacetylase, and acetate kinase of M. thermoacetica in the presence of 1 mg/L of Cu NPs decreased to only 70.1%, 69.3%, 50.1%, and 65.2% of the control, respectively. These results demonstrated that the release of Cu NPs in the environment could pose risks to anaerobic fermentation processes via regulating microbial transcriptional response and enzyme activity.

Comparative response of thermophilic and mesophilic sludge digesters to zinc oxide nanoparticles

The inevitable discharge of zinc oxide nanoparticles (ZnO NPs), from consumer and industrial products, into wastewater treatment plants (WWTPs) has created a need to determine their effect on sludge digestion. In this study, the effect of particle size (30 nm and 100 nm), type (coated and non-coated), and dose (6, 75, and 150 mg/g feed total solids (TS)) of ZnO NPs on anaerobic sludge digestion was studied under mesophilic (35 °C) and thermophilic (55 °C) conditions. The effect was investigated in two stages with different digester feeding regime: (1) batch biochemical methane potential (BMP) assays, and (2) semi-continuously fed reactors. Results showed that ZnO NPs were inhibitory at medium and high levels (75 and 100 mg ZnO/g TS, respectively). Coated NPs created less inhibition than non-coated NPs. Thermophilic bacteria were more sensitive to ZnO NPs compared with mesophilic bacteria. For the non-coated ZnO NPs, only the mesophilic batch assays were able to recover at the medium concentration and the thermophilic reactors presented chronic inhibition and could not recover. As a beneficial outcome, coated ZnO NPs significantly reduced odor-causing volatile sulfur compounds in digester headspace in comparison with the non-coated NPs. In summary, the condition in which ZnO NPs would have little to no effect would be 6 mg/g TS-coated ZnO NPs under mesophilic conditions.

Start-up Strategies for Anaerobic Ammonia Oxidation (Anammox) in In-Situ Nitrogen Removal from Polluted Groundwater in Rare Earth Mining Areas

The tremendous input of ammonium and rare earth element (REE) ions released by the enormous consumption of (NH4)2SO4 in in situ leaching for ion-adsorption RE mining caused serious ground and surface water contamination. Anaerobic ammonium oxidation (anammox) was a sustainable in situ technology that can reduce this nitrogen pollution. In this research, in situ, semi in situ, and ex situ method of inoculation that included low-concentration (0.02 mg·L−1) and high-concentration (0.10 mg·L−1) lanthanum (La)(III) were adopted to explore effective start-up strategies for starting up anammox reactors seeded with activated sludge and anammox sludge. The reactors were refrigerated for 30 days at 4 °C to investigate the effects of La(III) during a period of low-temperature. The results showed that the in situ and semi in situ enrichment strategies with the addition of La(III) at a low-concentration La(III) addition (0.02 mg·L−1) reduced the length of time required to reactivate the sludge until it reached a state of stable anammox activity and high nitrogen removal efficiency by 60–71 days. The addition of La(III) promoted the formation of sludge floc with a compact structure that enabled it to resist the adverse effects of low temperature and so to maintain a high abundance of AnAOB and microbacterial community diversity of sludge during refrigeration period. The addition of La(III) at a high concentration caused the cellular percentage of AnAOB to decrease from 54.60 ± 6.19% to 17.35 ± 6.69% during the enrichment and reduced nitrogen removal efficiency to an unrecoverable level to post-refrigeration.

Impacts of organics on the microbial ecology of wastewater anammox processes: Recent advances and meta-analysis

Anaerobic ammonium oxidation (anammox) represents a promising technology for wastewater nitrogen removal. Organics management is critical to achieving efficient and stable performance of anammox or integrated processes, e.g., denitratation-anammox. The aim of this systematic review is to synthesize the state-of-the-art knowledge on the multifaceted impacts of organics on wastewater anammox community structure and function. Both exogenous and endogenous organics are discussed with respect to their effects on the biofilm/granule structure and function, as well as the interactions between anammox bacteria (AnAOB) and a broad range of coexisting functional groups. A global core community consisting of 19 taxa is identified and a co-occurrence network is constructed by meta-analysis on the 16S rDNA sequences of 149 wastewater anammox samples. Correlations between core taxa, keystone taxa, and environmental factors, including COD, nitrogen loading rate (NLR) and C/N ratio are obtained. This review provides a holistic understanding of the microbial responses to different origins and types of organics in wastewater anammox reactors, which will facilitate the design and operation of more efficient anammox-based wastewater nitrogen removal process.

Linear anionic surfactant (SDBS) destabilized anammox process through sludge disaggregation and metabolic inhibition

The increase of emerging contaminants, such as surfactants, is one of the major challenges to biological wastewater treatment. However, the potential impact of linear alkylbenzene sulphonates (LAS), a major class of anionic surfactants, on anammox process is unclear. The long-term effects of sodium dodecyl benzene sulfonate (SDBS, as a model LAS) on reactor performance, microbial community and sludge properties were investigated in this study. The presence of 5 mg L^-1 SDBS promoted the release of extracellular microbial products from anammox granules and the wash-out of anammox population via effluent. Despite sludge disaggregation, the reactor performance was robust to the exposure of 5 mg L^-1 SDBS due to functional redundancy. With the further increase of SDBS to 10 mg L^-1, the metabolic activity of anammox biomass and the transcription and post-translation of hydrazine dehydrogenase were significantly decreased. The potential mechanism might be associated with the damage on cell membrane that induced the leakage of intracellular matrix. These results highlight the need to consider the potential risk of LAS to operation of anammox process in biological wastewater treatment plant.

Influence of biodegradable polybutylene succinate and non-biodegradable polyvinyl chloride microplastics on anammox sludge: Performance evaluation, suppression effect and metagenomic analysis

Microplastics (MPs) has been widely detected in wastewater treatment plants. However, there is a lack of research on its influence on anaerobic ammonia oxidation (anammox) process. Therefore, the effects of polybutylene succinate (PBS) and polyvinyl chloride (PVC) MPs on the nitrogen removal performance, microbial community and metabolites of anammox sludge were investigated. Results showed that PBS and PVC MPs reduced the nitrite removal efficiency of the anammox sludge, and PVC1 (0.1 g/L PVC) group was the most significant at 19.2 %. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra showed that PBS2 (0.5 g/L PBS) group increased the polysaccharide content in the anammox sludge. This may be because of the byproduct, which was produce during the biodegradation of PBS MPs, and decrease the agglomeration capacity of sludge, so as to increase the mass transfer. PBS2 group reduced the relative abundance of Methanosaeta (10.18 %) and the methane modules, and stimulated the anammox bacteria Ca. Brocadia (1.17 %) and the relative nitrogen metabolism modules. PVC2 group reduced the relative abundance of Ca. Brocadia (3.02 %), while was enriched Methanosaeta (2.1 %). Non-biodegradable PVC MPs was more harmful to anammox sludge, which would draw attention to the entry of PVC MPs into the anammox system.

Effects of ZnO nanoparticles on flocculation and sedimentation of activated sludge in wastewater treatment process

Despite the behaviors of ZnO nanoparticles (ZnO NPs) in wastewater treatment processes have been widely explored, the impacts of ZnO NPs on the activated sludge's flocculation and sedimentation performances for solid-liquid separation have rarely been involved yet. In this study, ZnO NPs were observed to exert a dose-dependent negative effect on the sludge's flocculation performance but did not significantly impact the sludge' sedimentation behaviors. Furthermore, it was NPs themselves rather than the dissolved Zn²⁺ who impaired on the sludge flocculation performance because the Zn²⁺ alone would not compromise the sludge's flocculation efficiency. In addition, the sludge flocculation performance was revealed to be inversely related to the extracellular polymeric substances (EPS) content in the sludge and the direct contacts between ZnO NPs and the cells in the sludge should be the prerequisite to stimulate the secretion of the sludge EPS. The poor sludge flocculation performance could also be caused by the reduced protein/polysaccharide (PN/PS) ratio and the zeta (ζ) potential in the loosely bound (LB-EPS) after the sludge exposure to ZnO NPs. Fourier transform-infrared spectra (FT-IR) and three dimensional - excitation emission fluorescence spectra (3D-EEM) analysis further revealed that the decrease of the tyrosine PN-like substance level in the LB-EPS was probably the key reason for the decreased PN/PS ratio and ζ potential in the LB-EPS, which eventually induced the decline of the sludge flocculation performance under the ZnO NP stress. These results could potentially expand the knowledge on sludge flocculation and sedimentation in the presence of ZnO NPs.

Exogenous Fe2+ alleviated the toxicity of CuO nanoparticles on Pseudomonas tolaasii Y-11 under different nitrogen sources

Extensive use of CuO nanoparticles (CuO-NPs ) inevitably leads to their accumulation in wastewater and toxicity to microorganisms that effectively treat nitrogen pollution. Due to the effects of different mediums, the sources of CuO-NPs-induced toxicity to microorganisms and methods to mitigating the toxicity are still unclear. In this study, CuO-NPs were found to impact the nitrate reduction of Pseudomonas tolaasii Y-11 mainly through the action of NPs themselves while inhibiting the ammonium transformation of strain Y-11 through releasing Cu²⁺. As the content of CuO-NPs increased from 0 to 20 mg/L, the removal efficiency of NO₃⁻ and NH₄⁺ decreased from 42.29% and 29.83% to 2.05% and 2.33%, respectively. Exogenous Fe²⁺ significantly promoted the aggregation of CuO-NPs, reduced the possibility of contact with bacteria, and slowed down the damage of CuO-NPs to strain Y-11. When 0.01 mol/L Fe²⁺ was added to 0, 1, 5, 10 and 20 mg/L CuO-NPs treatment, the removal efficiencies of NO₃^- were 69.77%, 88.93%, 80.51%, 36.17% and 2.47%, respectively; the removal efficiencies of NH₄⁺ were 55.95%, 96.71%, 38.11%, 20.71% and 7.43%, respectively. This study provides a method for mitigating the toxicity of CuO-NPs on functional microorganisms.

Insight into formation and biological characteristics of Aspergillus tubingensis-based aerobic granular sludge (AT-AGS) in wastewater treatment

The long start-up time and facile biomass loss of aerobic granular sludge (AGS) impede its application for actual wastewater treatment. The present study investigates a novel assist-aggregation strategy based on Aspergillus tubingensis (AT) mycelium pellets to accelerate sludge granulation, and engineered Fe₃O₄ nanoparticles (NPs) were used to further enhance flocculent sludge (FS) aggregation. The AT mycelium pellets, modified by 0.5 g/L Fe₃O₄@SiO₂-QC NPs (AT-V), had a more compact internal structure than the unmodified group (AT-I). The content of extracellular polymeric substances (EPS) and the zeta potential values were observed to increase from 39.86 mg/gVSS and -9.19 mv for AT-I to 69.64 mg/gVSS and 2.35 mv for AT-V, respectively. In optimized cultivation conditions, the aggregated sludge biomass of AT-V reached 1.54 g/g. An original AT-based AGS (AT-AGS) with a high biological activity (64.45 mgO₂/gVSS·h as specific oxygen uptake rate) and enhanced velocity (58.22 m/h) was developed in only 9 days. The removal efficiencies of total nitrogen (TN) and total phosphorus (TP) of the AT-AGS were 12.24% and 16.29% higher than those of the inoculated FS under high feeding load. Additionally, the analysis of cyclic diguanylate (c-di-GMP) and con-focal microscope images implied that polysaccharide (PS) of EPS played an important role in maintaining the stability of the AT-AGS. Finally, the dominant functional species contributing to sludge aggregation and pollutants removal of the AT-AGS showed a larger richness and diversity than those of the inoculated FS. This study might provide a novel high-efficiency strategy for the fast formation of AGS.

Responses of Anammox Granular Sludge to Long-Term Rare Earth Element Feeding: Lanthanum as a Case

A tremendous input of ammonium and rare earth elements (REEs) has entered the surroundings on account of the discharge and leak of leaching agents during rare earth in-suit leaching mining, which has threatened various organisms. Anammox has the potential to release nitrogen contamination, but the potential impacts of REEs on anammox bacteria remain unclear. In this study, La (III) was chosen as a case to explore the long-term impacts on anammox granular sludge. The 5 mg L−1 La (III) which was examined hardly affected the anammox granulates because of the defense of extracellular polymeric substances. The high La concentrations (10–50 mg L−1) caused intercellular accumulation and the significant inhibition of nitrogen removal performance and dehydrogenase activity, especially a decrease in the relative abundance of Ca. Kuenenia. Moreover, it also induced patently oxidative damage and affected cell membrane integrity. Notably, extracellular polymeric substances have a limited defense capability; neither La3+ nor Ca2+/Mg2+ efflux-related genes aggravated the intracellular accumulation of La.

The effects of silver nanoparticles on the microbial nitrogen cycle: a review of the known risks

The nitrogen cycle is an integral biogeochemical function for maintaining healthy environments. Nitrogen is a key nutrient that must be continuously replenished through recycling mechanisms to sustain ecosystems, disruption to which can result in compromised ecosystem functioning. Certain stages in the microbial conversion of nitrogen compounds are performed by a limited range of micro-organisms making these key functional species in ecosystems. The growing industrial use of silver nanoparticles (AgNPs) potentially poses significant risks for microbial nitrogen cycling species. AgNPs possess potent antimicrobial properties and are expected to reach a range of natural environments through several routes of exposure. Certain functional nitrogen cycling microbes have been shown to be highly susceptible to AgNP toxicity. The current literature indicates that AgNPs can negatively affect certain nitrogen fixing, nitrifying and denitrifying microbes in vitro. In vivo studies investigating the effect of AgNPs on nitrogen cycling microbial communities and nitrogen transformation rates in soil, sediment and sludge environments have also indicated disruption of these functional processes. This review provides a comprehensive description of the current state of knowledge regarding the toxicity of AgNPs to nitrogen cycling communities. The aim of the review is to highlight the most susceptible stages in the nitrogen cycle and the implications for the affected ecosystems.

Assessment of Anammox process against acute and long-term exposure of ZnO nanoparticles

The impacts of nanoparticles (NPs) on wastewater treatment have become a great concern because of their widespread applications. Although the acute responses of anammox bacteria to NPs have enhanced the knowledge about the potential risks of them, deep understanding of the cumulative impacts of NPs must be assessed. The purpose of this research was therefore to further extend the current knowledge by evaluating both acute and long-term effects of Zinc oxide (ZnO) NPs on Anammox process based on nitrogen removal performance, self-recovery ability and microbial community structure. The acute exposure tests indicated that, the median inhibition concentration (IC50) of ZnO NPs on Anammox process was 84.7 mg/L (54.82 mg ZnO NPs/g VSS). Acute exposure of 200 mg/L ZnO NPs (117.54 mg Zn/g VSS) caused 80% inhibition in batch assays while the long-term inhibition dosage was 100 mg/L ZnO NPs (187.50 mg ZnO NPs/g VSS) corresponding to 1022 mg/L total Zn (1916.27 mg Zn/g VSS) in the reactor due to the accumulation of NPs. Total, soluble and biomass-associated Zn concentrations were measured throughout the long-term exposure to observe the behavior of ZnO NPs in the reactor. Total Zn in the reactor was cumulatively increased and mostly originated from biomass-associated Zn. Following the long-term inhibition tests, self-recovery of Anammox process within 120 days demonstrated that, the ZnO NPs inhibition is reversible for the applied dose. Furthermore, next generation sequencing results indicated a symbiotic relationship between the microbial groups in the anammox bioreactor while relative abundance of Candidatus (Ca.) Brocadiaceae family showed a decrease parallel to the deterioration in nitrogen removal performance of bioreactor. At the end of the long-term exposure studies, 48.76% decline on anammox quantity was detected.

Resistance of anammox granular sludge to copper nanoparticles and oxytetracycline and restoration of performance

Nanoparticles and antibiotics, the two most frequently detected emerging pollutants from different wastewater sources, are eventually discharged into wastewater treatment plants. In this study, the widely used materials CuNPs and oxytetracycline (OTC) were selected as target pollutants to investigate their joint effects on anaerobic ammonium oxidation (anammox). The results indicated that the environmental concentration slightly inhibited the performance of the reactors, while the performance rapidly deteriorated within a week under high-level combined shocks (5.0 mg L^-1 CuNPs and 2.0 mg L^-1 OTC). After the second shock (2.5 mg L^-1 CuNPs and 2.0 mg L^-1 OTC), the resistance of anammox bacteria was enhanced, with an elevated relative abundance of Candidatus Kuenenia and absolute abundance of hzsA, nirS, and hdh. Moreover, the extracellular polymeric substance (EPS) content and specific anammox activity (SAA) showed corresponding changes. Improved sludge resistance was observed with increasing CuNP and OTC doses, which accelerated the recovery of performance.

Effects of zinc oxide nanoparticles on sludge anaerobic fermentation: phenomenon and mechanism

Zinc oxide nanoparticles (ZnO NPs) production and usage might lead to a large discharge of ZnO NPs into the natural environment, raising concerns of pollution and ecological security. The effects of ZnO NPs on waste activated sludge hydrolytic acidification and microbial communities were studied in semi-continuous fermentation systems. The fermentation performance of eight ZnO NPs concentrations including ZnO NPs normal [0.01, 0.1, 1 and 10 mg/g mixed liquor suspended solids (MLSS)] and ZnO NPs shock (10, 1000, 1000 and 10,000 mg/g MLSS) were discussed, and their biodegradability was also analyzed. The experimental results showed that proteins, polysaccharides and short-chain fatty acids were enhanced by ZnO NPs, particularly by ZnO NPs shock. Low ZnO NPs concentrations inhibited coenzyme 420 (F420) and dehydrogenase activities but enhanced α-glucosidase and protease activities. Illumina MiSeq sequencing revealed that ZnO NPs addition enriched Azospira, Ottowia and Hyphomicrobium but not Anaerolineaceae.

Copper oxide nanoparticles inhibited denitrifying enzymes and electron transport system activities to influence soil denitrification and N2O emission

Nanopesticides are widely applied in modern agricultural systems to replace traditional pesticides, which inevitably leads to their accumulation in soils. Nanopesticides based on copper oxide nanoparticles (CuO NPs) may affect the soil nitrogen cycle, such as the denitrification process; however, the mechanism remains unclear. Here, acute exposure experiments for 60 h were conducted to explore the effects of CuO NPs (10, 100, 500 mg kg^-1) on denitrification. In this study, Cu speciation, activities of denitrifying enzymes, electron transport system activity (ETSA), expression of denitrifying functional genes, composition of bacterial communities and reactive oxygen species (ROS) were determined. In all treatments, Cu ions was the dominant form and responsible for the toxicity of CuO NPs. The results indicated that CuO NPs treatments at 500 mg kg^-1 remarkably inhibited denitrification, led to an 11-fold increase in NO₃^- accumulation and N₂O emission rates decrease by 10.2-24.1%. In the denitrification process, the activities of nitrate reductase and nitric oxide reductase reduced by 21.1-42.1% and 10.3-16.3%, respectively, which may be a reason for the negative effect of CuO NPs. In addition, ETSA was significantly inhibited with CuO NPs applications, which reflects the ability of denitrification to accept electrons. Denitrifying functional genes and bacterial communities composition were changed, thus further influencing the denitrification process. ROS analysis showed that there were no significant differences among NPs treatments. This research improves the understanding of CuO NPs impact on soil denitrification. Further attention should be paid to the nitrogen transformation in agricultural soils in the presence of nanopesticides.

Response of nitrogen removal performance, functional genes abundances and N-acyl-homoserine lactones release to carminic acid of anammox biomass

Carminic acid (CA) can serve as a redox mediator and influence the electron transfer process. CA dosages of 0-5 mg/L were added to anaerobic ammonia oxidation (anammox) biomass. The results illustrated that CA not only reduced the inorganic nitrogen removal efficiency, but also decreased the nitrogen removal rate. The deterioration of nitrogen removal performance was due to the excess production of nitrate-nitrogen. The concentration of extracellular polymeric substances showed a decrease together with a decline in N-acyl-homoserine lactones release. CA addition decreased the activity of anammox bacteria while increasing the nitrifying potential. Quantitative reverse transcription polymerase chain reaction showed a decrease in anammox functional genes (nirS, hzo, and hzsB) and promotion of the expression of the nxrB gene, which corresponded with a decrease in anammox bacteria activity and the improvement of nitrifying potential. As a result, CA should not be added to anammox biomass.

Impact of adding metal nanoparticles on anaerobic digestion performance - A review

Anaerobic digestion is the most widely adopted biological waste treatment processes with renewable energy production. The effects of adding metal nanoparticles (NPs) on improving digestion performance are well noted. This paper reviewed the traditional view on the cytotoxicity of NPs to living organisms and the contemporary view of mechanisms for enhancement in anaerobic digestion performance in the presence of metal NPs. The complicated interactions acquire further studies for comprehending the physical and chemical interactions of metal NPs to the constituent compounds and to the living cells, and the involvement of mechanisms such as direct interspecies electron transfer for better design and control of the "NP strategy" for anaerobic digestion performance enhancement.

Long-term effects of copper nanoparticles on granule-based denitrification systems: Performance, microbial communities, functional genes and sludge properties

The widespread use of copper nanoparticles (CuNPs) has attracted increasing concern because of their potential effects on biological wastewater treatment. However, their effect on granule-based denitrification systems is unclear. Hence, the effects of CuNPs on denitrifying granules were investigated during long-term operation. The results showed that 51.9% of nitrogen removal capacity was lost after exposure to 5 mg L^-1 CuNPs, with the amount of Cu(II) gradually increasing with elevating CuNP levels. Moreover, the relative abundance of denitrifying bacteria (Castellaniella) and denitrifying functional genes (nirK, napA, narG and nosZ) obviously decreased. Meanwhile, the specific denitrification activity, the content of extracellular polymeric substances and dehydrogenase activity decreased by 44.0%, 15.2% and 99.9%, respectively, compared to their values in the initial sludge. Considering the downtrend in the abundance of copper resistance genes, it was deduced that the toxicity of CuNPs was mainly or at least partially due to the release of Cu(II).

Long-term impacts of carboxyl functionalized multi-walled carbon nanotubes on the performance, microbial enzymatic activity and microbial community of sequencing batch reactor

The performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were evaluated under long-term exposure of 0, 10 and 30 mg/L carboxyl functionalized multi-walled carbon nanotubes (MWCNTs-COOH). The presence of 10 mg/L MWCNTs-COOH displayed no adverse impacts on the COD and NH₄⁺-N removal of SBR, whereas 30 mg/L MWCNTs-COOH declined the COD and NH₄⁺-N removal. MWCNTs-COOH inhibited the denitrifying process and led to the accumulation of effluent NO₂^--N concentration. The inhibition of MWCNTs-COOH on the oxygen utilization rate, nitrogen removal rate and enzymatic activity of activated sludge gradually enhanced with the increase of operating time and influent MWCNTs-COOH concentration. MWCNTs-COOH stimulated more reactive oxygen species production and lactate dehydrogenase release, which might affect the microbial physiological functions and morphology. The microbial diversity and richness was declined evidently after long-term exposure of MWCNTs-COOH. The relative abundance of nitrifying and denitrifying bacteria showed some changes under MWCNTs-COOH stress.

More than sulfidation: Roles of biogenic sulfide in attenuating the impacts of CuO nanoparticle on antibiotic resistance genes during sludge anaerobic digestion

Biogenic sulfide (BS) in anaerobic digesters was previously suggested to mitigate the potential impacts of metallic nanoparticles (M-NPs) on antibiotic resistance genes (ARGs) propagation by sulfidation of the M-NPs. In this study, a new role of BS in regulating ARGs responses to M-NPs is reported. It was observed that CuO NPs at environmentally relevant level had no significant effects on the spread of ARGs. However, higher dosage (50 mg/gTSS) contributed to the propagation of ARGs, whose abundances would be effectively reduced by 74-115% if BS production was stimulated. Instead, introduction of EDTA, a metal ion chelator, resulted in much lower attenuation efficiencies (12-40%), indicating that restriction of the bioavailability of CuO NPs might not be the only reason for the buffering of ARG responses in the presence of BS. Further investigation showed that the presence of BS together with activation of key enzymes (O-acetyl serine sulfhydrylase and γ-glutamylcysteine synthetase) supplied and favored the biosynthesis and transformation of cysteine, which mitigated the oxidative stress induced by CuO NPs. Moreover, the amounts of cysteine and its metabolite glutathione in sludge were associated with the abundances of ARGs negatively, implying that in situ generated cysteine was the important ARGs regulator. Exploration of possible mechanisms revealed that the biosynthesized cysteine might limit gene transfer potential via mobile genetic elements, as cysteine restricted the abundances of intI 1, Tn916/1545 and ISCR 1. In addition, the cysteine remarkably alleviated the copper stress and copper resistance, which in turn blocked possible co-selection between copper and antibiotic resistance. This work provides new insight into attenuation of the bio-effects of NPs in digesters.

Biofabrication of Zinc Oxide Nanoparticles With Syzygium aromaticum Flower Buds Extract and Finding Its Novel Application in Controlling the Growth and Mycotoxins of Fusarium graminearum

Fusarium graminearum is a leading plant pathogen that causes Fusarium head blight, stalk rot, and Gibberella ear rot diseases in cereals and posing the immense threat to the microbiological safety of the food. Herein, we report the green synthesis of zinc oxide nanoparticles from Syzygium aromaticum (SaZnO NPs) flower bud extract by combustion method and investigated their application for controlling of growth and mycotoxins of F. graminearum. Formation of SaZnO NPs was confirmed by spectroscopic methods. The electron microscopic (SEM and TEM) analysis revealed the formation of triangular and hexagonal shaped SaZnO NPs with size range 30-40 nm. The synthesized SaZnO NPs reduced the growth and production of deoxynivalenol and zearalenone of F. graminearum in broth culture. Further analysis revealed that treatment of mycelia with SaZnO NPs resulted in the accumulation of ROS in the dose-dependent manner. Also, SaZnO NPs treatment enhanced lipid peroxidation, depleted ergosterol content, and caused detrimental damage to the membrane integrity of fungi. Moreover, SEM observations revealed that the presence of diverged micro-morphology (wrinkled, rough and shrank surface) in the macroconidia treated with SaZnO NPs. Taken together, SaZnO NPs may find a potential application in agriculture and food industries due to their potent antifungal activity.

Effects of ZnO nanoparticles on the performance of anaerobic membrane bioreactor: An attention to the characteristics of supernatant, effluent and biomass community

Two laboratory-scale anaerobic membrane bioreactor (AnMBRs) were built to investigate the effect of zinc oxide nanoparticles (ZnO-NPs) on their performance, and the recovery phase was also examined. Results showed that the addition of ZnO-NPs with 0.4 mg/L caused significant deteriorations of AnMBR performance, including decrements of chemical oxygen demand (COD) removal efficiency from 96.4% to 81.5% and biogas production from 0.36 to 0 L/g COD removal within 40 days. A significant increment from 13.2 to 52.1 mg/L in soluble microbial products (SMP) was obtained, while no obvious effect on colloids was observed except an increased fluctuation of colloid concentration. Additionally, gas chromatography-mass spectrometry (GC-MS) analysis revealed remarkable changes of compounds in effluent with exposure to ZnO-NPs, and some new alkanes and esters were produced, such as Cyclobutane, 1,2-diethyl-, trans-, Tetradecane, Cyclopropane, octyl-, and Butanoic acid, methyl ester. The microbial community was compared using high-throughput sequencing, clearly showing the changes in both bacteria and archaea communities. Furthermore, results for recovery phase indicated that the AnMBR performance can be recovered within around 60 days after stopping ZnO-NPs addition, accompanied by the decrement of zinc concentration mainly adsorbed by sludge.

Long-term impacts of graphene oxide and Ag nanoparticles on anammox process: Performance, microbial community and toxic mechanism

The increasing application of engineered nanoparticles (NPs) has posed an emerging challenge to constructed wetland wastewater treatment. The performance, microbial community and toxic mechanism of anammox-based unplanted subsurface-flow constructed wetlands (USFCWs) were investigated under the long-term exposure of different graphene oxides (GOs) and Ag NP concentrations. Results showed that the addition of GO could promote TN removal, manifesting as function anammox bacteria C. Anammoxoglobus having a relative high abundance, for GO did not cause significant damage to the cell integrity though there was an increase in ROS concentrations. TN removal would not be obviously affected under exposure of 1 mg/L Ag NPs, for the function gene related to cell biogenesis and repair was up-regulated; while the addition of 10 mg/L Ag NPs would have an inhibiting effect on TN removal in the USFCWs, for the disappearance of some species having anammox ability. Key enzymes of anammox process (NIR and HDH) decreased to some extent under GO and Ag NP exposure, and function gene of defense mechanisms had an increase trend in samples.

Evaluating the effects of Zn(II) on high-rate biogranule-based denitrification: Performance, microbial community and sludge characteristics

High-rate denitrification is a popular and efficient process for treatment of nitrate-rich wastewater. Knowing the effect of heavy metals on denitrification is essential for industrial development. In the present study, the long-term impacts of Zn(II) on denitrifying granular sludge were investigated. The suppression threshold of Zn(II) on denitrifying bacteria was 10 mg L^-1 for long-term exposure. The nitrogen removal rate was decreased by long-term addition of 10 mg L^-1 Zn(II). Castellaniella and Klebsiella were the two dominant genera under Zn(II) stress. The relative abundance of Klebsiella sharply decreased to 4.64% after the addition of 10 mg L^-1 Zn(II), whereas Castellaniella was susceptible to 2 mg L^-1 Zn(II), revealing that Castellaniella mainly was devoted to denitrification under no or low Zn(II) stress conditions, whereas Klebsiella was effective under high Zn(II) stress.